1. Field of the Invention
The present invention relates to a process, for obtaining plant a DNA fragment, which employs genetic engineering and molecular genetics and to a process for breeding plants, particularly forest trees, by using the plant DNA fragment.
2. Related Art
A typical method for breeding plants begins with selection of suitable individual candidates, by a skilled technician, based on observational data and analytical data for phenotypes. After the suitable individual candidates have passed an inspection test, they are preserved as official suitable individuals (registered species). It is also important to create progeny with new phenotypes by crossbreeding between the selected suitable individuals. Many existing plant species have a history of repeated selection and crossbreeding steps, but in the case of forest trees as an example, because of their long growth period, they have a very short history of crossbreeding, and therefore results still remain to be obtained in the future.
Most traits useful as a target of for breeding are a combination of many physiological phenomena (for example, the nature and density of the material, in the case of forest trees). It is thought that each phenomenon is defined by a corresponding genetic information of the individual (its genome), and is expressed when necessary. However, it is very difficult to accurately determine the actual key physiological phenomena and elucidate the interconnecting systems for each phenomenon. For actual breeding, it is common to describe a genetic lineage extending for a number of generations, and examine the progeny to determine useful traits. In addition to phenotypes, the molecular biological analysis data for enzymes and nucleic acids have recently come to be treated as one of the traits. This has led to a drastic increase in the number of markers on the genome, though in a random manner. By applying such numerous markers to certain genetic lineages and statistically processing the resulting polymorphic data, it has become possible to create specific gene linkage maps for those lineages. It is thought that if the markers are appropriately dispersed and abundant on the map, markers strongly linked with certain phenotypes can theoretically be found; that is, it is believed that trait judgments can be made on the statistical genetic level. However, so far, no reports have been published which use such molecular markers as selection references. The following problem is thought to be one of the causes for this.
The genome includes portions for specific genetic information (coding regions) and other portions [non-coding regions (characterized by a primary structure whose function is unknown, repeating or recurrent nucleotide sequences)]. The non-coding regions constitute the greater part of the genome, while the coding regions are scattered throughout the entire genome. Almost all of conventionally used molecular markers (particularly those derived from DNA) are acquired randomly, and most molecular markers are derived from such non-coding regions. That is, the existing molecular markers are ones that are unrelated to individual phenotypes. Thus, the differences in the genome between individuals and between species result in cases where the molecular markers cannot be universally applied. Specifically, since heterozygosity is recognized between individuals in most species including forest trees, when existing markers are considered for breeding applications, it is highly possible that they will only be effective when a specific individual is used as the parent material. To circumvent this situation it has been desired to obtain breeding markers that allow judgment of useful types and can be universally utilized without being dependent on heterogeneity.
It is an object of the present invention to isolate a DNA fragment derived from a gene or a group of genes linked with expression of a trait that serves as a breeding marker for plants. It is another object of the invention to provide a breeding method that utilizes a promoter sequence obtained by analysis of the aforementioned DNA fragment and employs such a DNA fragment as selection markers for breeding.